Microwave-induced plasma synthesis of Ag-doped ZnO nanoparticles: Modification in crystallography, defects, and bandgap

Abstract

Ag-doped ZnO nanoparticles were synthesized using a microwave-induced plasma (MIP) process, offering a rapid, energy-efficient, and environmentally friendly approach to tailoring ZnO's structural and optical properties. The effects of Ag doping (1, 3, and 5 at%) on crystallography, defect chemistry, and electronic transitions were systematically analyzed. X-ray diffraction (XRD) confirmed the formation of wurtzite ZnO with enhanced crystallinity and reduced microstrain. Especially, higher doping samples indicate the increase in the texture coefficient (TC). Rietveld refinement revealed minimal lattice distortions, while FT-IR and XPS analyses showed significant modifications in Zn–O bonding and oxygen vacancies (V_O) due to Ag incorporation. UV–Vis spectroscopy demonstrated tunable energy bandgaps, demonstrating a narrowing to 2.07 eV for 1 at% Ag doping due to defect-induced gap states and a widening to 2.56 eV for 5 at% doping due to the Burstein-Moss effect. Photoluminescence (PL) investigations revealed diminished defect emissions and reduced electron-hole recombination. The sample with 3 at% Ag doping exhibited optimal crystallinity and structural stability. These findings provide essential insights into the relationship between doping, defects, and bandgap modulation, serving as a guideline for optimizing ZnO-based nanomaterials for visible-light-driven photocatalysis and energy-efficient optoelectronic applications.